Memento Mori
Of the 8 designs for the WTC memorial, as much as I like the votive candles (a maintenance nightmare), my preference runs towards the outdoor designs (except the Mya Lin knock-off). Some of the indoor memorials are effective, evocative, emotive, etc., but they tend to make me feel a bit oppressed. And I'm not even a claustrophobe. Perhaps it would be different being there, and I concede a park-like setting might be less inspiring of reflection.